Visualizations typically consist of discrete graphical marks, such as symbols,
arcs, lines and areas. While the rectangles of a bar chart may be easy enough
to generate directly using SVG or Canvas, other shapes are complex, such as
rounded annular sectors and centripetal Catmull–Rom splines. This module
provides a variety of shape generators for your convenience.

As with other aspects of D3, these shapes are driven by data: each shape
generator exposes accessors that control how the input data are mapped to a
visual representation.